1. Field of the Invention
This invention relates in general to digital systems, and, more particularly, to touch screens used with digital systems.
2. Description of the Related Art
The usability of highly complex digital systems has been greatly simplified by the development of intuitive interfaces. Devices, such as touch screens, have helped to make it possible to utilize even the most complex digital systems by relatively untrained users. Touch screens have found application in a wide variety of complex systems, such as automatic teller machines, general purpose computers, manufacturing equipment, cash registers, etc.
Several technologies have been used to construct touch screens, such as, infrared transducers, ultrasonic transducers, and acoustic sensors. The acoustic transducers generate acoustic waves, for example, Rayleigh waves, shear waves, e.g., zeroth order horizontally polarized shear waves, or any other acoustic mode sensitive to touch. Acoustic sensor technology generally involves a plate, for example a glass plate that is exposed to an acoustic wave on either its surface (Rayleigh waves) or internal to the late (shear waves). When the plate is touched, some of the energy in the acoustic wave is absorbed, which can be detected and attributed to a particular location on the plate. Thus, the presence and location of a touch may be identified.
Both types of acoustic sensors have shown much promise, but both also have known shortcomings. For example, in Rayleigh wave technology the acoustic wave travels on the surface of the plate, and therefore, is greatly affected by an object touching the surface of the glass plate. Thus, even relatively light touches produce a substantial change in the Rayleigh wave, and may be readily detected. However, since the acoustic wave travels on the exposed surface it is also susceptible to environmental factors, such as dirt, dust, oils, water, etc. Accordingly, the use of Rayleigh wave technology may be limited to less severe environments, and may require frequent cleaning to insure proper operation.
In shear wave technology, on the other hand, since the acoustic wave travels within the glass plate, environmental factors have less impact on the ability of the system to detect touches. That is, dirt on the glass plate does not materially affect its operation. However, because the acoustic wave is within the glass plate, light touches have little impact on the acoustic wave, and, thus, are more difficult to detect. Substantially more pressure must be applied to a shear wave technology touch screen for a touch to be registered.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
In one embodiment of the present invention, a controller is provided to coordinate the operation of a touch screen. The controller includes at least an adjustable gain amplifier, and a control circuit. The adjustable gain amplifier has an input, an output, and a gain control terminal, and receives a first signal representative of an acoustic signal on a touch screen on the input terminal and delivers an amplified version of the first signal on the output terminal. The gain control terminal receives a control signal that varies the gain of the amplifier. The control circuit may include an analog to digital converter (ADC). The ADC receives at least a portion of the amplified first signal and outputs a digital signal (value) representative thereof. The control circuit may also include a processing element. The processing element is electrically coupled to the ADC and receives the digital signal. The processing element compares the digital signal to a preslected value and determines the difference if any between the digital signal and the preselected value. If the difference exceeds a preselected limit, the control circuit delivers a control signal to the control input of the amplifier. The control signal has a magnitude responsive to the determined difference.
Another aspect of the present invention provides a method for controlling the operation of a touch screen. An acoustic signal is delivered to the touch screen. The presence of the acoustic signal at the touch screen is detected and a first electrical signal responsive thereto is delivered. The first electrical signal is amplified by a preselected gain, and the amplified signal is digitized. Thereafter, a difference between the magnitude of the digitized amplified signal and a reference signal is determined, and the gain is varied in response to the difference.
In yet another embodiment of the present invention, a controller is provided to control the operation of a touch sensor system based upon predetermined parameters. This embodiment includes an adjustable gain amplifier and a control circuit. The adjustable gain amplifier has an input, an output, and a gain control terminal, and receives a first signal representative of an acoustic signal on a touch screen on the input terminal and delivers an amplified version of the first signal on the output terminal. The gain control terminal receives a control signal that varies the gain of the amplifier.
The control circuit includes at least a processing element and a memory element. The memory element stores data defining when the gain of the amplifier must be adjusted to compensate for variations in the manufacturing process of the touch screen used in the touch sensor system. Based upon this data, the processing element sends a gain control signal to the amplifier.